As petroleum-based materials escalate in price and environmental pressures increase, there is a growing need to responsibly utilize, to the greatest extent possible, all products from petrochemical processes, which includes the desired main products as well as co-products. Co-products are often treated as “waste” materials of no value.
It is known in the manufacture of adipic acid or caprolactam from cyclohexane that co-product streams result because the chemical transformations do not proceed perfectly in 100% yield. These co-product streams contain a variety of molecules having functionalities which include, among others, the alcohol, alkene, carboxylic acid, lactone, ester, and ketone groups. It is known to use some co-product streams for their fuel value. In such uses, there is no recognition or recovery of value for the functionality present in the co-product stream. As a result, most of the co-product stream from adipic acid manufacture remains underutilized.
Manufacture of adipic acid from cyclohexane generally involves two steps. First, cyclohexane is oxidized using air to a mixture of cyclohexanol (A) and cyclohexanone (K), the mixture being referred to as KA. Second, KA is oxidized using nitric acid to adipic acid. The current disclosure is focused on utilization of co-product streams from the first of these two steps, the oxidation of cyclohexane to KA. This “cyclohexane oxidation” step is also performed in manufacture of caprolactam from cyclohexane.
In the known cyclohexane oxidation processes, cyclohexane is generally oxidized with oxygen or a gas containing oxygen, at low conversion, to produce an intermediate stream containing cyclohexanol (A), cyclohexanone (K), and cyclohexyl hydroperoxide (CHHP) in cyclohexane. CHHP is an important intermediate in oxidation of cyclohexane to KA and various processes are known in the art to optimize conversion of CHHP to KA, in order to maximize yield of KA. In addition to K, A, and CHHP, cyclohexane oxidation produces co-products. In some cases, it has been found that these co-products interfere with subsequent processing to convert CHHP to KA. It is known that at least some of the interfering co-products can be removed by contacting the intermediate stream containing K, A, and CHHP with water or caustic, for example as described in U.S. Pat. No. 3,365,490, which is incorporated herein by reference. This contacting, or extraction results in a two-phase mixture that, after phase separation, yields a purified cyclohexane stream containing K, A, and CHHP (which can be subjected to known high-yield processes to convert CHHP to KA) and a co-product water stream. The co-product water stream (“Water Wash”) contains various mono- and di-acids, hydroxy-acids, and other oxidation co-products formed during the initial oxidation of cyclohexane.
Regardless of whether water wash is performed as an intermediate step, the stream containing K, A, and CHHP is further processed by methods well known in the art, to complete conversion of CHHP to K and A. The resulting mixture is then refined, again by methods well known in the art, to recover unconverted cyclohexane for recycle and to obtain purified K and A for subsequent oxidation to adipic acid or conversion to caprolactam. The high-boiling distillation bottoms from this refining operation are known as non-volatile residue, “NVR.”
To summarize, the co-product streams, sometimes referred to herein as “by-product” streams, available from a cyclohexane oxidation process include “Water Wash” (the aqueous stream produced by water extraction of cyclohexane oxidate) and “NVR” (the high-boiling distillation bottoms from KA refining). Concentration of Water Wash by removal of at least some of the water produces a stream known as “COP Acid.”
“Water Wash”, “COP Acid”, and “NVR” are known to contain both mono- and poly-functional materials, mainly with the functional groups comprising acids, peroxides, ketones, alcohols, and esters. Other functional groups such as aldehyde, lactone, and alkene are also known to be present. Multiple functional groups may be combined in a single molecule, such as in a hydroxyacid, for example hydroxycaproic acid or hydroxyvaleric acid. In general, the acid functional group is at one end of a linear hydrocarbyl chain, and the hydroxy group may be present in various positions along the chain. Known examples of hydroxyacids include 6-hydroxycaproic acid, 5-hydroxyvaleric acid, 3-hydroxyvaleric acid, and 3-hydroxypropionic acid. Similarly, known examples of simple mono-acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, and caproic acid. Known examples of diacids include succinic acid, glutaric acid, and adipic acid. Known examples of keto-acids include 4-oxo valeric acid (also known as levulinic acid) and 5-oxo caproic acid. Known examples of alcohols include cyclohexanol, 1-propanol, 1-butanol, 1-pentanol, and various diols such as 1,2- 1,3-, and 1,4-cyclohexanediols, various butanediol isomers, and various pentanediol isomers.
The chemical complexity of “Water Wash”, “COP Acid”, and “NVR” introduce difficulties to obtain pure, commercially-useful chemicals from these streams. Efforts to develop processes to obtain useful materials from these streams are known and varied.
In view of the foregoing disclosures, it would be desirable to provide a simple process for the recovery of ester-based solvents from “Water Wash”, “COP Acid”, and/or “NVR” which uses economically sound and practical high recovery means. It would also be desirable to provide an effective solvent or novel chemical intermediate.